Special Weather Statement, NWS Eureka, CA

AREA FORECAST DISCUSSION
National Weather Service Eureka CA
252 PM PDT Tue Sep 5 2017

.SYNOPSIS...Relatively cool temperatures will prevail across the
area through Friday. In addition, showers and thunderstorms will
be possible, particularly during Thursday. Warmer and drier
conditions are forecast to return Sunday into Monday.

&&

.DISCUSSION...An upper-low was positioned 300 miles SW of San
Francisco this afternoon, with several minor spokes of augmented
ascent rotating cyclonically around it. One spoke in particular
was moving north across the central Sierra Nevada Mountains, and
was aiding in the development of a large cluster of thunderstorms.
Short term model guidance indicates this activity will spread
northwestward toward northwestern CA tonight...mainly in the form
of non-thundering showers.

Subtle shortwave ridging is forecast to occur in the wake of the
showers during Wednesday, which will likely suppress
shower/thunderstorm development for most locations in NWRN CA.
Thereafter, model guidance shows a PV filament detaching from the
northern stream, and then digging toward CNTRL portions of
coastal CA. As this takes place, the previously mentioned upper
low ejects north across NWRN CA. The ejecting wave will aid in
increased shower/embedded thunderstorm coverage over the area
during Thursday.

After Thursday, a trough located offshore will support near
normal temperatures over the region Friday and possibly Saturday.
During Sunday, upper heights are forecast to build as another
upper low forms offshore from SRN CA. As that occurs, low-level
flow will become north-northeasterly, resulting in moderating
temperatures and a drier weather pattern Sunday into early next
week.

&&

.AVIATION...The main "somewhat" flight hazard of lately has been
the huge amount of smoke influx from wild fires across the
region. However, some smoke dispersal today caused visibilities to
improved at the main airports. Conditions were greatly improved
as mid level moisture streamed into the areas and smoked aloft
thinned out...although smoke advection still remained heavier in
the Northern-most areas. Even so, expect the smoke to continue
through the TAF period. Noticeably, a thin strip of stratus
developed along the Southern Humboldt/Northern Mendocino Coast
today. The North Coast may see limited fog develop "if" overnight
temperatures cool more than the last previous days. Models
certainly are suggesting some lower Vis/Cigs in the morning.
Interior Mendocino will stay VFR, but for all locations, an
increase in combined upper level dynamics suggest The possibility
of thunderstorm/shower activity (a flight hazard) tonight into
Wednesday. /TA

&&

.MARINE...Southerly winds and seas are generally light this
afternoon with waves only around 3 to 4 feet. Most of these waves
are around 10 to 14 seconds. The strongest winds and wind waves
are just south of Cape Mendocino. Local south winds of 20 kt are
expected just downwind from the cape.

Light southerly winds will persist through Wednesday as the upper
level low approaches the area the. On Thursday as this lows
starts to move across the area winds will become northerly once
again. Northerly winds will start to increase on Friday and Into
the weekend as high pressure builds into the area. Small craft
advisories will likely be needed by late Friday. Winds will remain
elevated through the weekend and into early next week, but gale
warnings are not expected at this time.

Currently there is a southwest swell moving into the waters. It
is currently around 2 feet at 14 seconds. This is expected to
generally persist over the next several days. Tonight a
northwesterly swell is expected to start building into the waters.
Initially it will be around 1 to 2 feet at 16 seconds building to
around 4 feet at 14 seconds. This will slowly drop to around 12
seconds by Thursday. /MKK

&&

.FIRE WEATHER...An upper-level trough slowly approaching the
region from the south will aid in maintaining relatively cool
afternoon temperatures through Saturday. As a result, minimum RH
values over interior areas will be fairly moist. In addition, isolated
showers and thunderstorms will be possible tonight into Wednesday.
Coverage will then increase on Thursday as an upper disturbance
moves north across the area. At this time, wetting rainfall
appears probable during Thursday. Warmer and drier conditions
appear likely Sunday into Monday as low-level winds become
northeasterly.

SMOKE...Visible satellite imagery shows expansive smoke cover
located from northern Humboldt and Trinity counties into Del Norte
county. Weather conditions will not change substantially through
Wednesday...thus smoke coverage/density will likely be similar to
today. In addition, showers appear likely during Thursday, which
may aid in dispersing the smoke somewhat. Thereafter, north-
northeast winds are forecast to develop Sunday night, which could
cause smoke to spread toward the coast once again.

&&

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...None.
NORTHWEST CALIFORNIA COASTAL WATERS...None.
&&

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For forecast zone information
see the forecast zone map online:
http://www.weather.gov/eureka/zonemap.png

Hazardous Weather Outlook
National Weather Service Eureka CA
139 PM PDT Tue Sep 5 2017

CAZ101>108-111-062045-
Coastal Del Norte-Del Norte Interior-Northern Humboldt Coast-
Southwestern Humboldt-Northern Humboldt Interior-
Southern Humboldt Interior-Northern Trinity-Southern Trinity-
Northeastern Mendocino Interior-
139 PM PDT Tue Sep 5 2017

This hazardous weather outlook is for northwest California.

.DAY ONE...This afternoon and tonight.

Showers and isolated thunderstorms will be possible tonight. In
addition, smoke dispersion will improve somewhat tonight due to
cooler temperatures and southerly winds.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Showers and thunderstorms are forecast to increase in coverage during
Thursday. In addition, smoke dispersion will continue to improve
through Friday. Thereafter, offshore winds during Sunday night and
Monday may cause smoke to spread toward the coast once again.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.

CAZ109-110-112-113-062045-
Mendocino Coast-Northwestern Mendocino Interior-
Southwestern Mendocino Interior-Southeastern Mendocino Interior-
139 PM PDT Tue Sep 5 2017

This hazardous weather outlook is for northwest California.

.DAY ONE...This afternoon and tonight.

No hazardous weather is expected.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Showers and thunderstorms are possible during Thursday.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected at this time.

Special Weather Statement
National Weather Service Eureka CA
835 PM PDT TUE SEP 5 2017

CAZ103-106-060400-
Northern Humboldt Coast CA-Southern Humboldt Interior CA-
835 PM PDT TUE SEP 5 2017

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL HUMBOLDT COUNTY
UNTIL 900 PM PDT...

At 834 PM PDT, Doppler radar was tracking a strong thunderstorm near
Eureka, moving northwest at 25 mph.

Pea size hail, winds in excess of 30 mph, and occasional cloud to
ground lightning strikes will be possible with this storm.

Locations impacted include...
Eureka, Arcata, Myrtletown, Cutten, Fairhaven, Humboldt Hill, Pine
Hills, Freshwater, Bayview, Samoa and Kneeland.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Occasional cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4084 12421 4091 12418 4075 12396 4064 12406
      4074 12428
TIME...MOT...LOC 0334Z 128DEG 23KT 4074 12413

BC